Unsteady cooling problem with conduction and two-phase radiation are numerically analyzed here for a spherical two-phase (gas-particle) medium exposed to the rarefied cold environment. Two-phase radiative transfer equation (RTE) affected by both gas and particle phases is taken into consideration. This nonlinear integro-differential RTE is solved by using the discrete ordinates method (DOM, or the so-called SN method). A parametric study is performed by changing the conduction-to-radiation parameter, optical thickness, convection-to-radiation parameter, gas and particle absorption-to-extinction ratio, wall emissivity and heat capacity ratio. Thermal characteristics are discussed through spatial temperature distribution, transient mean temperature variation, and radiative heat loss. The results confirm the significant effects of the two-phase radiation on the unsteady thermal characteristics for two-phase medium.